This invention relates to improvements in the method of making a Raney nickel catalyst.
Raney nickel catalysts are well known hydrogenation catalysts, and supported catalysts of this material have been formed by a number of methods. Goldberger, U.S. Pat. No. 3,637,437 discloses flame spraying Raney catalyst material onto a substrate and then leaching the aluminum from the alloy. While the catalytic structures produced by this method are highly active, they are subject to spalling during the activation step, and the process is labor intensive and hence relatively costly. In addition, the mode of application often results in severe distortions of non-rigid substrates due to non-uniform heating.
Another method proposed involves forming a layer of aluminum and nickel and the interdiffusion of these metals to form a catalyst layer at the interface. Nickel can be the substrate, or can be applied as a layer to a substrate by electrodeposition, flame spraying, vapor phase deposition, or other suitable means. U.S. Pat. No. 3,846,344 to Larson et al. exemplifies this prior art, and shows interdiffusion of aluminum and nickel at a temperature below the melting point of aluminum.
Under these temperature conditions the alloy Ni.sub.2 Al.sub.3 is produced as a major product. This is undesirable in that it is difficult to activate during the subsequent leaching operation with aqueous sodium hydroxide solution. The desired phase, NiAl.sub.3, which is readily activated and is the precursor to the active catalyst, is formed in a thin layer (about 0.025 mm) between the Ni.sub.2 Al.sub.3 and the Al. Catalysts prepared by the low temperature interdiffusion process are therefore relatively short lived because of the thin layer of active catalyst produced.